Yeah this is a very valid point. If you're in it to collect, then stamina refills are the worst thing (or I guess second worst thing compared to a raid point refill) you can spend gems on, unless it's to complete an event that's about to end, since they give no permanent value other than letting you reap the rewards of a stronger team sooner (like earlier 12-5 farming, but 12-5 farming doesn't help you get 5-stars+).